A large-scale pipeline test rig at Deltares, Delft, The Netherlands has been used for filling and emptying experiments. Tests have been conducted in a horizontal 250 mm diameter PVC pipe of 258 m length with control valves at the downstream and upstream ends. This paper investigates the accidental simultaneous closure of two automatic control valves during initial testing of the test rig. The simultaneous closure of both valves has induced upsurge and downsurge at the same time. Large water

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... er and column separation have caused failure of pipe supports and leakage at pipe joints. The incident was caused by a fault in an electronic conversion box due to power failure. Afterwards the downstream end automatic valve has been modified to a manually operated valve to avoid the accidental simultaneous closure of the valves. The accidental transient event has been fully recorded with pressures, flow rates and water levels. The measurements of the accident are presented, analyzed and discussed in detail. Photographs show the damages to the system.